Diagnostic evaluation of dementia in Denmark

The validity and quality of the diagnostic evaluation of dementia in the secondary health care sector in Denmark is high-lighted in two registry-based studies. A third registry-based study focuses on the development in diagnosing dementia in the Danish secondary health care sector from 1970 to 2004.

Validity of dementia diagnoses in the Danish hospital registers

The validity of dementia diagnoses in the Danish nationwide hospital registers has been evaluated in a random sample survey. Two hundred patients were randomly selected from 4,682 patients registered for the first time with a dementia diagnosis in the last 6 months of 2003. One hundred and ninety-seven journals were available for review to evaluate if they fulfilled ICD-10 and/or DSM-IV criteria for dementia and specific dementia subtypes. Fifty-one patients who were still alive in 2006 were interviewed.

The registered diagnosis of dementia was found to be correct in 169 (86%) cases. However, regarding dementia subtypes, the degree of agreement between the registers and the results of the validating process was quite low (overall agreement calculated as kappa statistics was only 0.36 (95% CI 0.24-0.48)).

The study concluded that the validity of an overall dementia syndrome in the Danish hospital registers is high, thus supporting the reliability of epidemiological studies about dementia. Alzheimer's disease seemed to be under-diagnosed but also had a good validity once the diagnosis was registered. Other ICD-10 dementia subtypes in the registers (vascular dementia, frontotemporal dementia) had a low validity and are less suitable for epidemiological research.

Diagnostic evaluation of dementia in the Danish secondary health care sector

The quality of diagnostic evaluation for dementia in the secondary health care sector in Denmark has been evaluated in a nationwide registry-based study. The study sample were the same two hundred patients that was randomly selected for the above-mentioned study. Through medical record review the completeness of the diagnostic work-up was evaluated, using evidence-based dementia guidelines as reference standards.

Satisfactory or acceptable completion of the basic dementia work-up was documented in 51% of the patients. Only 12% of those with unsatisfactory work-up were referred to follow-up investigations. An overall dementia syndrome was confirmed in the majority of the cases, but correct subtypes were diagnosed in only 35% (cf. the above-mentioned study).

The study concluded that the adherence to clinical guidelines concerning dementia work-up is inadequate in the secondary health care sector. The findings of the study emphasize a need for improvement in the organization of clinical dementia care, for education of dementia specialists and for changes in attitude towards making a diagnosis of dementia.

Time trend in diagnosing dementia in the Danish secondary health care sector

The trend of diagnosing dementia in the secondary health care sector over time is evaluated in a nationwide longitudinal study of the incidence and prevalence of registered dementia diagnoses in the Danish national hospital registers.
All Danish residents born before 1964 and alive at their 40th birthday were followed from their 40th birthday (or from January 1, 1970, whichever came later), to the date of the first dementia diagnosis recorded in the hospital registers, the date of emigration, date of death, or December 31, 2004, whichever came first. Age- and period-specific incidence and prevalence of dementia were calculated.
The Danish study population consisted of 4,723,838 persons with 81,090,583 person-years of follow-up. 154,152 dementia cases were registered from 1970 to 2004. The incidence and prevalence of registered dementia diagnoses showed an increasing trend over time. A marked improvement in the diagnostic rate of dementia in secondary health care over time was shown indicating that this sector can be an important point of entry for patients with dementia in Denmark.

In 2003 the Danish hospital register data on the incidence and prevalence of dementia diagnoses were about 33% lower than estimates from large European community-based cohort studies (EURODEM). This discrepancy can be partly explained by the fact that some of the diagnostic workup is done by general practitioners (primary health sector). The discrepancy, however, may also reflect a tendency to under-diagnose dementia. If the Danish hospital register data are compared with higher and more up-to-date European estimates on dementia prevalence (EuroCoDe or World Alzheimer Report 2009) the discrepancy is even more pronounced.